Question: $\left(-10x - 6\right)\left(-9x + 5\right) = \ ?$
Answer: $= -10x \cdot \left(-9x + 5\right) - 6 \cdot \left(-9x + 5\right)$ $= \left( -10x \cdot -9x \right) + \left( -10x \cdot 5 \right) + \left( -6 \cdot -9x \right) + \left( -6 \cdot 5 \right)$ $= 90x^2 + \left( -10x \cdot 5 \right) + \left( -6 \cdot -9x \right) + \left( -6 \cdot 5 \right)$ $= 90x^2 + \left( -50x + 54x \right) + \left( -6 \cdot 5 \right)$ $= 90x^2 + 4x + \left( -6 \cdot 5 \right)$ $= 90x^2 + 4x - 30$